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DevotedSkeptic writes with an interesting article on possible lighting sources for growing food on the moon and other off-world locations. From the article: "... Agriculture remains the key to living and working off-world. All the mineral ore in the solar system can't replace the fact that for extended periods on the Moon or Mars, future off-worlders will need bio-regenerative systems in order to prosper. Here on earth, researchers still debate how best to make those possible, but nuclear-powered state of the art LED technology is arguably what will drive photosynthesis so necessary to provide both food and oxygen for future lunar colonists. ... Although during the two weeks that make up the long lunar day astronauts might be able to funnel refracted sunlight into covered greenhouses or subsurface lava tunnels, they will be left without a light source during the long lunar night. Current solar-powered battery storage technology isn't adequate to sustain artificial light sources for two weeks at the time. Thus, the most practical solution is simply to use some sort of Radioisotope Thermoelectric Generator, not unlike the one powering the current Mars Science lab, to power the LEDs that will spur photosynthesis in lunar greenhouses. ... On earth, Mitchell says it takes roughly 50 square meters of agriculture to provide both food and oxygen life to support one human. But, as he points out, who can say how productive plants are ultimately going to be on the moon, in gravity that is only one sixth that of earth?"

Gravity isn't a problem, that's not what the article is about. The article is talking about how NASA is finally researching LED-powered greenhouses to provide light for plants in a lunar environment, even though greenhouses on earth have already been doing it for at least a decade. There are also high-hundreds/low-thousands of marine aquarists out there that have been doing it for some time, using red-blue LED panels to grow turf algae in their sump tanks for nitrate export.

Gravity isn't a problem, that's not what the article is about. The article is talking about how NASA is finally researching LED-powered greenhouses to provide light for plants in a lunar environment, even though greenhouses on earth have already been doing it for at least a decade. There are also high-hundreds/low-thousands of marine aquarists out there that have been doing it for some time, using red-blue LED panels to grow turf algae in their sump tanks for nitrate export.

That may not be the point of the article, but it does flat out question how plants will grow in low gravity. It's even in TFS:

But, as he points out, who can say how productive plants are ultimately going to be on the moon, in gravity that is only one sixth that of earth?

To me the real early steps to progress would not involve the Moon or Mars, but space stations with artificial gravity and radiation shielding.

Then you can actually have people, animals, plants etc living AND reproducing in space as opposed to trying not to degenerate so fast.

Trying to settle on the Moon and Mars without such stuff is like trying to jump before even being able to stand.

So from my perspective NASA etc nowadays are mainly a waste of resources. They're not really working on the necessary steps for the long term survival of the species in space. They're just sending expensive toys to mars and other places.

p.s. fish would probably do ok in low gravity, and some live on algae which doesn't need very much. You're going to want to have tons of water around anyway, so might as well put fish in at least some of it and filter the water when you want to use it for other stuff.

So from my perspective NASA etc nowadays are mainly a waste of resources. They're not really working on the necessary steps for the long term survival of the species in space. They're just sending expensive toys to mars and other places.

I dunno. I think a lot of the stuff they do is a waste of money (the ISS, anything to do with sending humans into space) but they're the only ones doing anything at the moment. That alone is worth $5/person/year.

Trying to settle on the Moon and Mars without such stuff is like trying to jump before even being able to stand.

I'd argue entirely to the contrary: Open space, from anywhere in high-enough-so-the-atmosphere-doesn't-get-you earth orbit out to the darkest edges of nowhere where Azathoth lurks in the dark places between the stars, is about as hostile an environment as one can reasonably imagine operating. Other than a reasonably steady supply of photons there is nothing there that you didn't bring with you(at considerable cost).

By contrast, any planet that isn't actively trying to murder you(eg. Venus and Mercury probably aren't at the top of the list) has massive amounts of potentially useful elements in the same gravity well as you. Just lying there for the taking. An overwhelmingly less hostile situation; but with more scientific novelty than just building a mockup in some place cold and dusty.

Satellites are crazy useful to the inhabitants of the planets that they orbit; but actually putting humans on them is a waste of time and space(with the one quite specific exception of doing low and zero-g medical research, which you can't easily do under other circumstances.

If you want cool planetary research, spewing robots at interesting planets is very likely the cheapest way to get it. If you want human populations that aren't on earth, colonizing objects that come with large amounts of free matter, and maybe even an atmosphere, rather than building teeny little bubble-capsules is overwhelmingly more practical. If you want to do research on long-term closed-system design and engineering, it's probably a waste to leave earth at all. Just buy up a bunch of warehouse space somewhere cheap, and you can run a dozen simultaneous experiments on earth for less than you could a single experiment in earth orbit(plus, if something goes wrong, you can just scrub the experiment, open the door, and resupply from home depot, rather than having to resort to mass deaths or heroic measures....)

Really, the only reason to have humans in open space for any nontrivial period of time would be research on how to deliver them reasonably safe and intact to an eventual planetary colony elsewhere(which may or may not actually involve sending humans at all. If team biotech can get amniotic tubes working, there would be some major benefits in just shipping a big cryo-flask full of iced zygotes, rather than dealing with adult astronauts....)

I don't see the point of spending lots of resources leaving a somewhat hospitable gravity well just to get stuck in an inhospitable one. You are still going to need most of the tech you need in a space station to survive on Mars or the Moon. You can't step outside and live for long on both places. And I doubt the winds and dust storms on Mars will be that helpful. Vast expanses of low productivity[1] inhospitable land isn't what I call a benefit. Even worse if you need idiocy like LED lights for the plants

I don't see the point of spending lots of resources leaving a somewhat hospitable gravity well just to get stuck in an inhospitable one. You are still going to need most of the tech you need in a space station to survive on Mars or the Moon. You can't step outside and live for long on both places. And I doubt the winds and dust storms on Mars will be that helpful. Vast expanses of low productivity[1] inhospitable land isn't what I call a benefit.

That's pretty much what most of the earliest floating algae in the sea might have said to the first plants that put their roots up into the dry land and populated previously-unknown continents with their progeny; and what later sea-dwelling critters might have said to the first fish-thing that decided to use its fins to slither out onto the unpopulated land surface, that by then had developed into a huge new ecosystem, ready for animals to enjoy and exploit. And thus, after many revolutions around the sun,

You miss my point completely.I'm saying staying in "open space" + asteroids will be better than trying to stay on Mars, the Moon and the other places where you can't have near Earth gravity, and even ignoring that are about as problematic as staying in "open space" - you still have to build your habitats and everything - except the Moon and Mars are further away than a space station that you can more conveniently build near the earth, and then move to where you want in the solar system (e.g. to an asteroid)

Can't do it in reverse. Need to build the first few stations near the earth. For testing (we haven't even got a space station with artificial gravity yet! Think about how much time and resources we've been wasting) and also the first few mining and manufacturing ones. Chicken and egg and all that.

Once things are going, then sure most will be built near/on the asteroids. That's what the space colony thing is all about anyway.

Exactly! We should be setting up a farm on the moon. Just to test it out. Start small: 1 m2 of soil in a greenhouse.

The cost of such a mission is for a small part related to the cost of the boosters to get things in orbit and to the moon, and for a large part to the over-engineering that NASA is doing. That over-engineering is caused by a fear of failure. It's not like it's rocketscience to get anything to the moon. The fear of failure is the only thing that seems to hold us back.

If it costs 5000 $/kg to launch anything into a high orbit (which I will equate with getting it to the moon), a decent sized farm (1000 tons of material) would cost 5 billion $ in launch costs, which is nothing.

We could set up some practice greenhouses for a fraction of the cost. If failure is an option, that should be cheap enough in an age when more than that is spent on warfare every day...

We haven't even been able to successfully create a small, enclosed, self-sustaining biosphere environment here on earth. If we can't even do it *here*, how is there going to be any progress in doing it on the moon?

My thought is, don't try to make a permanent self-sustaining biosphere right off the bat. Start by trying to keep things alive for, say, a lunar month. Learn from that, and try for two months. Learn, rinse, repeat. A single experimental bio-sustainability probe could perhaps perform such experiments a dozen times over a year or so using the same materials. (Question - use hydroponics, or soil-based growing medium?) Learn what is missing. It might be best to start with something simple such as simple

Regardless of the size of your lunar farm, you will still need to provide light to the plants during the two weeks of darkness that is the lunar night. Further, if you are going underground to protect yourself, and the plants you live on, from radiation, then you will need to provide all the light all the time.

You've touched on a very important point. There has been a lot of work on this topic. For small diameters the spin rate is so high that the coriolis force on your body is disruptive - your feet want to go one way, your head in another. The centrigugal force is also different at the feet and the head. And the stars would be going by outside the window (if there are any) at rather startling rates.

So 200-300 meters becomes the most reasonable minimum radius. According to NASA via Wikipedia [wikipedia.org]:

Turning one's head rapidly in such an environment causes a "tilt" to be sensed as one's inner ears move at different rotational rates. Centrifuge studies show that people get motion-sick in habitats with a rotational radius of less than 100 metres, or with a rotation rate above 3 rotations per minute. However, the same studies and statistical inference indicate that almost all people should be able to live comfortably in habitats with a rotational radius larger than 500 meters and below 1 RPM. Experienced persons were not merely more resistant to motion sickness, but could also use the effect to determine "spinward" and "antispinward" directions in the centrifuges.

Oh rly? Use enough Tesla power packs and they'll be fine. Lithium is light.

I was thinking the other day about a thermal accumulator - dig a hole, build what basically amounts to an insulated vessel, heat it up during the solar day, and during the solar night, use the accumulated heat to power some heat engines. On a larger scale, it should be more efficient than batteries (the larger the vessel, the smaller the heat loss compared to the total capacity).

Hmm.... so many problems, where to begin...1. 50 square meters of vegetation per person. HOw are you going to build a structure large enough to do all your planting?2. I see the snark remarks about getting your centrifuge spinning in a vacuum but you are providing oxygen and food. how are you going to get oxygen and food in and out with out appreciable loss of energy? (and gardeners, fertilizer, seeds. wait, where is the fertilizer coming from? capturing the astro port a potties will help but you will ne

The moon and Mars have gravity - albeit less than Earth. No idea whether that's enough.

OTOH I wonder how well those plants do in absence of a complete ecosystem. Thinking of our own bodies, we have more foreign microbe cells in our gut than we have cells of our own. Without those bacteria we can't survive, we need them to digest our food. Healthy soil, the kind that provides nutrients to plants, is also teeming with microbial and insect life. I really wonder how well plants do without all those other life f

The dutch have years of experience with hydroponic farmhouses and it works well enough for them to sell vegetables all over Europe. The downside is that some of them TASTE more like water than like the fruit they're supposed to be, but that most likely is due to selection on how they look in the grocery store. (You've usually already bought them when you get to the taste)

I know about hydroponic farming, and that's likely the way any extraterrestrial farming would go.

But the ones we have now are still in our ecosystem, not in an absolutely sterile environment like on the Moon. That may prove a key difference. These baths or glass fibre mats or whatever they use the roots are hanging in will contain lots of bacteria they picked up from the environment, totally naturally. What these bacteria do I don't know but good chance they do influence growth.

Bacteria that break down organic matter into ammonia, then ammonia to nitrite then nitrite to nitrate would be important if you're trying to compost waste. But, see, the thing is, bacteria are pretty light and can grow pretty quickly. If you wanted to do this you would't actually need to keep sendig bacteria up there.

Not that you'd actually need it to grow plants, just to compose waste back into fertilizer. Initially, you'd send up a few tons of fertilizers to get going but that's a one time deal. Eventuall

If you build a habitat at one of the lunar poles it will be possible to build photovoltaic power plants which are both in sunlight and close enough to the habitat to directly feed power to it with electricity transmission lines. Additionally, this makes it easy for a habitat to be accessible for polar orbiting spacecraft. Habitats anywhere else on the moon move way from the orbit of your vehicle with the rotation of the moon. If your landing site is on the equator, then you can use an equatoral orbut, but for landing sites away from the poles or equator the orbitor continually moves away from the landing site, requiring that place correction manoeuvres be done before landing or docking with a returning vehicle.

First, I've never heard the 50 sq meters (538 sqft) to sustain 1 human before. It's about the same area as an ultra-efficiency apartment. I assume that's for high-efficiency hydroponics. Interesting. I wonder if it'd be possible to grow some sort of edible algae to suppliment the more traditional crops? IE have an intense 2 week growing season, harvest when the sun goes down, then reseed when it comes back up? That would reduce the need to use your nuclear generator to keep the plants alive/in the proper growing cycle.

The gravity might mean you needing a slightly different breed, but given what I've seen with hydroponics/areoponics, I doubt that 1/6th gravity will have that much of a negative effect - but that would be something for the ISS to figure out!

Wasn't proposing shutting down the RTG, more 'you need a smaller one for the number of people you have". If you can get 50% of your food and O2 needs from the algae, that's 50% fewer other crops you need. I mentioned algae because it's about the shortest lifecycle for photosynthetic Iife I know. I don't know of any other food crops that can handle 2 weeks of light followed by 2 of night.

Anyway the reason congress keeps denying funding to try making more P-238 is they just want NASA to find a way of using P-239 instead. That will also solve the problem of there being tons of the stuff in storage we have no need for.

The only reason they use P-238 at present is because of it's shorter half-life and the fact that it only gives off alpha particles which are relatively e

Only 1/6th gravity, no atmosphere - why not use mirrors? You can afford some inefficiency, such cheap materials would mean you don't need to worry too much about replacement costs due to meteorite hits.

It doesn't always have to cost gazillions - I refer you to the Russian use of pencils..:)

I love when wise guys link to that article without bothering to read it or to understand the significance.

Lead pencils were used on all Mercury and Gemini space flights and all Russian space flights prior to 1968

The lesson being that low tech worked just fine.

And if we're going to actually get out there and stay in space, then we need to be able to make do and get by. Apollo 13 was fixed with duct tape and a sock. The ISS is currently screwed because they can't get a single bolt to turn and are paralyse

The ISS is currently screwed because they can't get a single bolt to turn and are paralysed with indecision:

They stretched the space walk an extra hour and forty five minutes to try and fix the bolt.Nothing they tried worked, so NASA told the astronauts to strap the box down and leave it for the next scheduled spacewalk.

I'm not sure how you took those facts and ended up at "paralysed with indecision."

Notice the reasons that NASA was interested in a pen: Pencils could break and cause a hazard, and additionally were susceptible to a fast burn in the oxygen rich environment.

Pencils worked. They didn't work "just fine" they were a hazard, but nobody has a better system, until the pressurized pen.

While high tech for its own sake can be a bad idea often there's good reasons for new technology. The old tech may work but the new tech works better, more efficient, more reliable, less dangerously, etc.

As a simple example you've probably used, take optical mice vs ball mice. Yes ball mice work, however they have numerous problems. Optical mice work better. They are less susceptible to dirt, easier to clean, track on more surfaces, work at all angles including upside down and so on. As an extension, newer ones are getting even better, they have greater precision, track on even more surfaces, and so on.

So if you want, you can heat your water in your low tech "works just fine" fire pit with wood and a metal bucket. I think I'll heat mine in my high tech sealed water heater that is very efficient, safe, and convenient, because it works better.

The ISS is currently screwed because they can't get a single bolt to turn and are paralysed with indecision

It's not indecision, it's the terminal disease that modern NASA is infected with. Everything is done for PR and to justify funding, and so instead of looking to accomplish substantive missions, everyone is just going around trying to not get fired. Missions are all based on how much PR they'll generate and how safely and easily they can be done, rather than the substance of what they'll actually accomplish. No one wants to make any decision with any real risk.

The ISS is neither screwed nor paralyzed with indecision. They have the luxury of time, they are not in any immediate danger, and they have an escape pod back to Earth. The situation is in no way analogous to Apollo 13.

The Russians did use pencils, but what the legend fails to mention that they could do that because they didn't use a pure oxygen athmosphere, unlike the Americans. Graphite in oxygen was a fire hazard for them.

In fact current hydroponic systems reduce that space needed by 1/4. If money was actually spent on research they could further reduce the space needed to process Co2 and generate O2 by using plant material.

And WHY use nuclear powered? we could easily put up solar farms. yes you have to deal with the face that the lunar days are 28 earth days but storage can deal with that. You dont have weather to contend with, so every day period will be a perfect charging period.

I couldn't give you numbers but I can tell you that given how a fair bit of vegetative food/herb crops don't require much in the way of light (300-500umol) we don't have to worry much about power if we utilize LED. Also, newer systems currently in design are specifically made to grow the same area with (in my current tests) with half of what typical LED lighting would need.

On top of that, many have proposed excellent power sources. RTG are one idea, and we can use the lunar sub-surface as a heat sink. Nucle

This is all about the moon's 14-day, Lunar–night power famine. The solution is simply to use solar power satellites [wikipedia.org] sitting at one of the Earth-Moon Lagrangian points, where the solar collectors will be in perpetual sunlight. Perpetual power means always-on growing lights so the problem is solved without the need for RTGs, and their pretty horrible thermal inefficiency (not to mention the problem of where do you get all that Pu239 from).

The main problem with using solar power satellites for supplying power to the Earth (the huge cost of launching them into space) is neatly inverted in the Lunar context as, by placing a solar colony's power hardware in space, you have a large mass of hardware that doesn't have to be soft-landed on the moon, representing a substantial saving.

The 50 Sq meter comment bugs me. Its not like we are plowing the back 40 with mules. By now can't we think more 3d? if 50 sq meters would feed one human, how many humans would 1000 cubic meters feed (10x10x10 room)? A greenhouse dedicated to growing could have walls, even the ceiling used for growing. My imagination can think of many other problems, but in a low gravity environment space should not be one. If fact, why not have a module orbiting the Moon that is specific to growing food and just use g

Current solar-powered battery storage technology isn't adequate to sustain artificial light sources for two weeks at the time.

This is simply wrong. Rechargeable batteries can easily hold a charge longer than two weeks. And once you have that, you have the ability to sustain light sources on battery power for two weeks.

Thus, the most practical solution is simply to use some sort of Radioisotope Thermoelectric Generator, not unlike the one powering the current Mars Science lab, to power the LEDs that will spur photosynthesis in lunar greenhouses.

No, it isn't. RTGs are limited by heat dissipation. Put enough isotope in one place and it heats up enough to melt. More and it'll eventually vaporize or perhaps even achieve criticality (such as the case with plutonium 238). A traditional nuclear plant scales better at high power levels.

There is a huge issue with scale here. Lets do some rough calculations. A person needs 50^2 m of green space lit 1/3 of the time. To duplicate sunlight, we need about 1kW/m^2. Assume we have an LED that is about 10% efficient. That comes out to about 167kW per person. RTG like those on deep space probes have outputs measure in Watts, not kilowatts. RTGs don't scale well. If you need these kinds of outputs, you will be looking at conventional reactor. Getting rid of the excess heat is going to be a real chal

Actual research with LEDs, which can selectively emit light in the bands actually used for photosynthesis, suggests that the amount of electricity required for illumination is in the order of 1000 watt/m^2 period, no "factor of 10" multiplier needed. So 50 KW is needed continuous (no, you don't turn the lights off for most crops - only photoperiod sensitive ones light strawberries).

Unless we are talking about a three-person station here, this is absurd. How much power is required for something large with 100-200 people? Megawatts, I am sure. For thermal stability you will want the entire complex to be underground - the surface of the moon swings between +200F in sunlight to -200F without sunlight, either in shadows or during the night period.

So we are talking about lighting for 200 people. And ventilation. And water pumps for drinking water, toilets, etc. So, thousands of large,

If you're setting up a farm on the moon, do you pressurize it to the equivalent of our atmosphere at sea level, or will half an atmosphere suffice? Do you use the same mixture that makes people comfortable, or do you bump the CO2 up to 10 or 15%? Do you use nitrogen, helium, or whatever you can cook out of the rocks to make up the rest of it? What about humidity? Temperature?

If all you want is visible light, then an RTG is a horribly inefficient way to get it. As has been previously suggested, a full-blown fission reactor is a bit of a problem due to heat dumping and safety. Why not take the middle ground?

Use a powerful alpha-only emitter such as Gd-148 and a mix of phosphors to give you the spectrum and intensity you need. Alpha particles are stopped by almost anything, and as long as you don't inhale/ingest them, they're relatively harmless. Since you're talking a space environment and can generally trust the astronauts to not make too many errors in judgement, you could even use a beta emitter with a little shielding. We already have the phosphors to generate RGB, unless we've forgotten how to make them (think CRT - the electron gun is nothing more than an electronic beta emitter).

Generating electricity with existing RTG technology is about 5% efficient [wikipedia.org]. This paper [cormusa.org] mentions phosphored white LEDs efficiencies at 55 Lm/W. This paper [ucl.ac.uk] says "The efficiency of the color phosphors was experimentally compared within the range up to 90 Lm/W for green, up to 30 Lm/Watt for blue, and up to 35 Lm/Wt for red color at 14 kV." [In this case kV are keV since they were shooting electrons]. This site [lbl.gov] says the decay energy of a Gd-148 alpha particle is about 3.271 MeV.

The DOD is looking at some thorium reactors. By having small ones (10 MWe) they can bring these in via chopper, put them in a hole, and then provide power for bases, esp. FOB. These would then be easy to destroy if being overrun. Now, what is the advantage of this for the moon and mars? Ppl do not get too upset about thorium being sent up to space. The amount of uranium that would be needed to power it would be minimum. And one of the nice advantages is that the thorium reactor in sodium would have little to no chance of water in either locations. In addition, the 800C can be used not just to provide power, but also a number of chemical reactions and industrial operations (i.e. metal smelting for casting purposes). In addition, it provides the heat for the base without needing any real shielding.

I mean, I grow some plants that require lots of sunlight but that for reasons beyond my power cannot be cultivated in the open air.

If the NASA sends me a couple of these atoms, I can assure them that I will use them on my plants, that I will keep a serious control of its growth and that I will tell them if some unexpected toxic byproduct appears in them.

If you need to grow plants for food/oxygen off-world, that means you have people there.
If you have people there, that means they're going to be doing other stuff.
If they're going to be doing other stuff, that means they're going to need power.

If they're going to need power, you should just have a power generator which pumps out electricity, and channel some of that electricity to the LEDs providing light for your hydroponics lab. There's no need to put an RTG inside each LED.

Especially considering that most of the energy given off by an RTG is thermal (the RTG aboard Curiosity gives off about 2 kW of thermal energy, about 110 W of which is converted to electricity). With an RTG inside each light source, every minor light source is also a major heat source, and your heating/cooling problems become that much more complicated. With all your power centralized in a few places (for redundancy), you can centralize heat pumps which deliver only as much heat only where needed.

The reason they taste like crap is not just because they were transported, but because they are varieties that have been selected for their longevity so that they can be transported.

Given that the tomatoes will probably be left on the vine until they are consumed, there's no reason to use the crappy modern supermarket tomato varieties - they can use heirloom breeds [wikipedia.org]. There's always been a high emphasis on morale considerations in the American space programme, and food has always been one of the things that t

The "it's on the dark side of the moon so it can never be seen" idea doesn't really hold up to much scrutiny. A few humans (some still alive) saw the dark side in the late 1960s/early 1970s and more recently the LRO is imaging the surface in a detail that even Apollo astronaut tracks can be seen as well as some of the discarded hardware (and I don't just mean what landed, some bits ended up there after being discarded from lunar orbit).

One could say "Well duh, the base is underground!" but then every single

There are resources of Uranium and Thorium on the moon itself, so it may be possible for lunar nuclear power to be self-sustaining. Of course, nuclear reactors need other materials as well, and I'm not sure if some of those would have to be brought in from earth (such as coolant in the form of water, sodium, or salts).

B. "Now LED's are at about 100 lumens per watt" - WRONG AGAIN. We have 5500K white LEDs with 150+ lumens per watt, and Cree has already broken 220+ lux/w - LAST YEAR.

C. "So you need about 1,300 watts to light up one square meter to the same intensity as sunlight. Very roughly." Sure, but you're implying most of our food crops even need that sort of intensity - they don't.

D. "Solar cells and inverters and wiring have an end-to-end efficiency of around 10%" Yea, if you use cheapo garbage. The stuff powering my research facility, end-to-end, pushes roughly 22%.

E. "So we need about 13 meter-square panels at right-angles all the time to the Sun to get 13,000 watts during sunny days on the Moon." I see you totally ignore the fact that our moon has no atmosphere worth mentioning, so that photon flux density is actually much higher versus on earth, you also forget that the moon is closer to the sun then we are roughly half of the time, so again, the photon flux is even greater.

G. "And oh, where are you going to get the water for 50 square meters of whatnot growing?" Plenty of hydrogen and oxygen on the moon, plus we've found water there. We can make fake snow by just expelling compressed hydrogen and oxygen in a shared jet nozzle (it's how we make snow during the summer on mountain ski resorts) so I bet making water from scratch components would not be that difficult. On top of that, we've got hydroponics systems that can drop water requirements as much as 99% for many crops.

Your numbers fail to take into account how plants grow and just how much space is needed.

And as an aside - I [tinypic.com] do [tinypic.com] this [imgur.com] professionally. [imgur.com] I'm going to have to say your words are sorely lacking in knowledge on the relevant subjects.